New product and processes for producing same



Patented Apr: 13, 1937 NITED STATES "PATENT OFFICE.

New rnonuo'r AND rnocassns roa rno- DUCING SAME James E. Kirby,Wilmington, DeL, assignor to E. I.

duPont de Nemours &' Company, Wilmington, Del., a corporation ofDelaware No Drawing. Application November 2, 1931, Serial No. 572.7 39

9 Claims. .(l.18--58) ing polymers very sfihilar to those of chloro-2-This invention relates to processes for treating synthetic latices, andto products prepared by such processes. More particularly the inventionpertains ,to the use of'dipping 'meth production of formed articles fromlatices containmg halogen-2-butadiene-L3 polymers.

, Prior art It has been discovered, as disclosed by Carothers andCollins in application #490,538, filed October 22, 1930-, now U. S.Patent No. 1,950,431,, that hydrogen halldessuch as hydrogen chlorideand hydrogen bromide may be made to combine with monovinylacetylene'under suitable conditions with the formation of chloro-2- butadiene-l,3and bromO-Z-butadiene-LB respectively. By way of illustration, theydescribed the formation of chloro-2-butadiene-1,3 by passingmonovinylacetylene .into an aqueous solution containing 0 hydrochloricacid, cuprous chloride, and ammonium chloride, the two l ftst-namedcompounds acting in conjunction as a preferred catalyst for thereaction. They/further showed, as de- [2 February 28, 1931, nowU. S.Patent No. 1,950,432, that chloro-2-butadiene-L3 may be polymerizedunder a variety of conditions, e. g., by the use of elevated temperatureand/or elevated vpressure, air, oxidizing catalysts, and light, to yieldproducts closely resembling vulcanized natural i rubber in theirphysical properties. It was fur- 3 ther shown by Williams in application#519,244, filed February ,28, 1931, now U. S. Patent No. 1,950,436, thatother polymers of chloro-Z-butadiene-l.3 can be prepared by stopping thepoly- .merization before it goes to completion, and while the polymersare still plastic, which polymers possess the properties of unvulcanizednatural rubber, maybe utilized'and fabricated in 4 the y. ndfinallyconverted by H into products closely resembling vulcanized naturalrubber. It has been further shown by Collins in application #537,484,filed May 14, 1931, now

S.'Patent 'No. 1,967,861,, that chlord-2-butadime-1,3 is readilyemulsified inwater and, after polymerization in this state, yields anartificial latex from which, a material very similar to naturalvulcanized rubber may be obtained by coagulation or evaporation. Finallyit has been discovered by Carothers and Collins as disclosed and claimedin application #537,492, filed May 7,14, 1931, now U. SQlfatnt Nol1,950,433, that;

.bromo-2-butadiene-1,3 maybe subjected to the 55; processes of the abovecited applications, yieldods for the scribed and claimed in application#519,243, filed butadiene-1,3 already described. While the rubber-likeproducts obtained by complete polymerization either in emulsion or inmass or by heating the plastic polymers of the type discovered byWilliams very closely resemble vu1'-- canized natural rubber in, most oftheir physical and mechanical properties, they are in certain respectsmarkedly superior. For example, they are only very slightly swelled byaliphatic hydrocarbons such as gasoline, and are much more resistantthan natural rubber to the action of ozone. v

It has been proposed in numerous patents to prepare articles of naturalrubber by coagulation or other means directly from natural rubber latex.In order for these articles to have the pensive, also introduces sulfuror similar compounds which in general darken the product,

produce an unpleasant odorand taste, and also cause tarnishing ofcertain metals such as copper and silver in contact with the rubber. Inaddition to these objections, freshly coagulated natural rubberis veryweak and consequently thread, ribbons, and thin sheets preparedtherefrom require special, care in handling before vulcanization. r

' Objects of the invention Objects of this invention are therefore toprovide a. method for the production of articles directly fromartificial latices prepared from halogen-2-butadiene-l,3, e. g.,chloro-2-butadlone-1,3 and bromo-2-butadiene-L3 and to produce formedarticles which have the desirable properties of natural vulcanizedrubber, and are in addition light in color,..free from objectionabletaste. and odor, have no tarnishing action,

and furthermore are highly resistant to swelling bysuch substances asgasoline, and highly resistant to deterioration by agents such as ozone.

'A further object of the invention is to provide for the manufacture offormed elastic articles directly from artificial latices by processeswhich do not require vulcanization orthe introduction of sulfur orsulfur compounds and in which the freshly coagulated rubber is noteasily damaged. A specific object or the invention relates to theDescription of the invention A dispersion of polymerized chloroor bromo-2butadiene;l,3,,liereafter referred to as synthetic latex, is subjectedto conditions which bring about the separation of the rubber-likepolymer from the liquid phase oi the disper-- sion in the form ofelastic articles of the desired shape. This is accomplished inaccordance with the teachings of the present invention by dipping .aform having the shape and size corresponding to that which it is desiredthat the final'product assume, into a latex of halogen-2-butadiene-1,3polymer, withdrawing zothe form slowly-from the latex and coagulatingthe coating of latex either by "allowing the, filmto dry at ordinary orelevated temperature or by dipping the form into a suitable coagulatingbath,- washing and drying the film or coating, and then stripping itfrom the mold. In order to obtain smooth and uniform coatings by thisprocess, it is necessary to observe certain precautions, since simplelatices prepared from halo gen-Z-butadiene-Lli sometimes fail to wetsolid surfaces uniformly. This difllculty may be overcome in the processof the present invention by various methods. Thus, it has been foundthat if the concentration of the latex is such that it contains morethan 55% by weight of polymerized halogen-2-butadiene- 1,3 it wets'solidob-' jects readily and forms uniform continuous films. .The same object,namely, the modification of the latex so as to make it capable ofwetting solid objects uniformly and producing uniform, 4 continuousfilms, can be accomplished by adding to the latex small amounts, e. 2.,.2 to 2% of protective colloids such as polyvinyl alcohol and especiallyof proteins, such as casein or glue. When this method is used it is notnecessary to have the latex more concentrated than 55% and, indeed,latices of any desired concentration may be used.

articles by dipping followed, by coagulation Formation of (made, forinstance, of glass or glazed porcelain or polished wood) by dipping theform in the latex and withdrawing it slowly andat an even speed. Thecoating of latex is'then coagulated by dipping in a coagulating bathsuch as a mixture of one volume of ordinary concentrated hydrochloricacid and four volumes of ethyl alcohol or by exposing to a coagulant,such as hydrogen chloride in the vapor phase or a saturated solution ofsodium chloride. After washing off the excess of coagulant with water,an additional layer of the polymer may be applied over the first by arepetition of the same procedure. This is continued until the desiredthickness is obtained. The coagulated material is then dried on the formand finally stripped.

The coagulation may be assisted, if desired, by maintaining thecoagulating bath at elevated temperature which is above room temperatureand below the boilingpoint of the coagulating medium. The coagulationmaylilgewise be as- .latex as in the sisted by maintaining the coatedform at'a similar elevated temperature either before or duringdeposition of the latex on the form.

Formed objects may also be formed by alternate and repeated dippings inseparate dispersions of chloro-2-butadiene-L3 polymer and vulcanized orunvulcanized natural rubber or other synthetic rubber.

Exnmmra Use of acid later The above procedure may be varied as follows:A layer of the alkaline latex used in Example 1 is applied as above andthen dipped into an acidic latex made as described in Example C below.Mutual coagulation of the acid and alkaline latices results. Thisprocess of adding first a layer of alkaline, then a layer of acid latexmay be continued until the desired amount of material is deposited. Thecoating is then dried and removed as described above.

Instead of using a glazed form as in Examples 1 and 2, the form may becoated with parafiin before dipping in the latex, or the form maybecomposed entirely of paraifin or some other low melting material such asWood's metal. The adhering coagulated layer may then be readily removedby warming to soften the paraflln, -or other low melting material. Inall cases the latex may be applied to the form by spraying or othermeans instead of dipping.

Articles of varying shapes may be made by this method. For instance,tubing may be made by repeatedly dipping twine which is coated withparaflln into the latex and coagulating after each immersion. Afterdrying, the finished tube may be readily removed. Sheets may be made byforming a coating upon a cylindrical mold and then cutting itlongitudinally.

EXAMPLE 3 Formation of by evaporation Instead of coagulating thesuccessive coats of preceding example, the polymer may be precipitatedin continuous form by allowing the water to evaporate at eitherordinarly or elevated temperatures. Multiple layers of the polymers maybe readily built up in this way if the dried coat of polymer is firstwet with a wetting agent such as an aqueous solution of a salt of anisopropyl naphthylene sulfonic acid to assist the wetting of the driedpolymers by the succeeding coat of latex.

EXAMPLE 4 Removal of water by auction Formed articles may also beprepared by dipping porous molds in the synthetic latex and thenremoving the water by applying suction to the present invention may beprepared as follows:

Exxmmn A Preparat on of standard latex Four hundred grams ofwater'containing 8 g. of dissolved sodium oleate is rapidly stirred bymeans of a mechanical stirrer and 400 grams of chloro-2-butadiene-L3 isthen added slowly articles by dipping followed sion results. Thisemulsion is then maintained at 10 C. for 48 hours or until thepolymerization of the chloro-2-butadiene-1,3 is substantially 5complete.- The resulting pure'white, fine dispersion of polymerizedchloro-2-butadiene-L3 is treated with 16 golf ordinary concentrated am-'monium hydroxide solution and then with 4 g. ofphenyl-beta:liaphthylamine which is first dis:

lopersedin water by grinding in'a ball, mill with sodium oleatesolution. The resulting compoundeddispersion is strained thru a finecloth to remove any large solid particles and is thenready for use. i

l 1 It is usually more desirable to use a latex more concentrated than,that of Example A: Such a latexmay be prepared as follows:

EXAMPLE B Preparation of concentrated lat-e05 The procedure of Example Ais followed exactly I EXAMPLE Preparation of acid latea:

One-half gram of casein is dissolved in 26 g.'of glacial acetic acid and65 g. of water. Twenty- 40 three grams of chlord-2-butadiene 13 is thendispersed in thissolution in the same manner as in the sodium oleatesolution used in the preparertions above. In about twodays thepolymeriza tion is complete anda latex,. similar in appearance'to thosedescribed above, results;

'Anacid latex which may also be used in the process described inExample. 2 may be made from the standard latex by adding to 100 grams ofthe latex 5g. of gelatin dissolved in 100 g. of water 50 and then addingenough acetic or sulfuric acid to cause the latex to turnCongo testpaper blue. In addition. to the dispersion described above. a greatvariety of latices may be used satisfactorily in' the practice ofthisinvention.- Thus any 55 of the latices disclosed in Collins U. S.application #537,484, cited above.-may in general be used. These laticesinclude those preparediunder high pressure and attemperatures above C.and those in which alkalies, catalysts, inhibitors of 60 polymerization,and solvents for the chloro-2- 'butadiene-i,3 are present during thepolymerizatlon. included volatile solvents such as benzene,,soi'tenerssuch as those used in the rubber and nitro- 5 cellulose. arts, andsubstances which are them:

selves capable oi polymerization such as isoprene, styrene, and vinylacetate. Furthermore, as dis closed in the above cited application,other modifylng agents'such as proteins, pectins, and water- 7Q solubleresins may be added either before or after the polymerization of thechloro-2-butadiene-l,3.

Dyes, pigments, and fillers of the. type used'in;

rubber compounding may similarly be dispersed with thechloro-2butadiene-1',3 before'its poly-v 75 merization or may be addedafterwards, .The

. sion of a plastic polymer. which resemble natural rubber latex veryclosely,

, may be used in the practice of the present inven-" Under theclassification of solvents are.

V 2,o7e,e49 3 with constant stirring. A homogeneous emulsynthetic latexmay also be mixed with natural rubber latex or similar aqueousdispersions. Un-

usuallystrong and tear-resistant articles may be obtained if salts ofwater-soluble alkyd resins, that is, syntheticresins formed by partialesterification of a polybasic acid with a polyhydric alcohol which mayalso be partly esterified by other acids, are used as dispersing agentsinstead of the sodium 'oleate specified in the above descriptions of thepreparationof the synthetic latex. Unusually pliable products may beobtained if a small quantity, for instance 1-2%, of dlchloro-2,3-butadiene-1,3 is added to the chloro-2-buta- I dime-1,3 beforepolymerization, as disclosed in the copending application of Carothersand Berchet, Serial No. 589,052, filed January 26, 1932,

. now U. S. Patent No. 1,965,369.- Stlffer products.

which are desirable for some purposes are made from the standard latexdescribed above. Still stiffer products are made by first incorporating,

proteins, especially glue, into the latex.

As has been disclosed in U. S. application #537,484, the addition ofcertain inhibitors of polymerization, such as iodine, to the chloro-2-butadiene-VLB before emulsification brings about formation under certainconditions of a disper- Such dispersions,

tion to yield variously formed articles composed of plastic syntheticrubber.

Since this plasticity is retained for long periods, such articles may besubjected to further molding or coalescing operations long after theirpreparation. Hence, the plastic material thus obtained by coagulation ismore applicable to certain manufacturing operations than is the elastic,fully cured polymer which has already been described and which isplastic and cohesive for only ashort time after its coagulation. Theplastic articles obtained by coagulation or other means may be convertedto the elastic non-plastic insoluble state by heating, preferably in thepresence of curing agents."

such as zinc oxide,- which may be incorporated by dispersion in waterand mixing'with the dispersion of polymerbefore the latter iscoagulated.

It is desirable in all cases to prevent the oxidation of the syntheticrubberyarticles by the addition of antioxidants of tlue type used withnatural ing. It is also advantageous to have present in the syntheticrubber articles some substance to combine with traces of hydrogenchloride which are sometimes evolved from the rubber on long standing.Such substances are bases. or substances capable of combining withacids. Zinc oxide has been found useful for this purpose.

As coagulants, acids, or salts dissolved in water,

or in neutral liquids which are miscible with water, for example ethylalcohol and acetonemaybe used. Small concentrations (2% or-less) 0f evenweak acids such as acetic acid, are sufll-' cient for coagulation, whilehigher concentrations of salts are necessary, for example, that presentin a saturated aqueous solution of sodium chloride. Nonaqueoussolventsand concentrated salt solutions exhibit a dehydrating effect onthe coagulum in addition "to the'coagulating action.

Ordinary concentrated hydrochloric acid in alcohol, saturated solutionof sodium chloride in watern 10 g In addition to the advantagesdiscussed above, the molded articles prepared according to thisinvention are unexpectedly much stronger than those obtained fromnatural latex and stronger than articles of polymerizedchloro-2-butadi'ene- '1,3 or brmo,-2-butadiene-1,3 prepared by othermethods. Furthermore, the method of the present invention for theformation of articles by dipping and coagulation is much simpler thanthat to which natural latex must be subjected, in that the syntheticlatex need not be concentrated, its' coagulation and setting is muchmore rapid, may be accomplished at room temperature by means of a greatvariety of coagulating media and the resulting articles haveconsiderable strength, even immediately after coagulation, and areconsequently much more readily subjected to further operations.

The above examples 'have been directed specifically to the treatment orlatices of chloro-2- butadien'e-La polymer. Theinvention is likewiseapplicable to the similar treatment of laticesof otherhalogen-2-butadien'e-L3 polymers, e. g.,

bromo-2-butadiene-L3 polymer, the slightly different conditionsnecessary for the treatment of the latter latex being easilydeterminable by simple experiment in the light or the present invention.

'It should pointed out that it is by no means obvious that the syntheticlatices described herein would behave similarly to natural rubber latex,since it differs from the latter in many respects; for example itsparticle size is much smaller, in general it contains no proteins orresins, and its particles are composed of solid polymer rather than asemi-fluid interior surrounded by a thin sack as is believed to be. thecase with natural rubber latex. Furthermore, it

is quite unexpected that the freshly precipitated, material shouldremain temporarily plastic and.

cohesive. The much greater wet strength freshly coagulated-chloro-2-butadiene-1,3 polymer compared with that of freshly coagulatednatural rubber could not be foreseen. Furthermore, the

great strength oi-the' dried coagulated polymer scope of the claims.

as compared with that of chloro-2-butadiene-1,3 polymer prepared byother methods is entirely unexpected.

The above description and examples are illus- 'trative only and are notto be construedas limiting the scope of the invention. Any variationtherefrom which conforms to the spirit of the in-- vention is intendedto be' included within the I claim:

1. In the process for the preparation of shaped articles from syntheticlatex, the steps which comprise dipping a form of predetermined size andshape into a body of a synthetic latex comprising more than 55% byweight oi! dispersed chloro-2-butadiene-L3 polymer, then withdrawing theform slowly and at an even speed from the body of the latex, therebyretaining a coating of latex on the form and removing thedispersingmoving the dispersing medium from said coating.

3. The process of claim 2 further characterized in that the colloid is aprotein.

4.:The process of claim 1 further characterized in that theconcentration of polymer in the body of latex is 57 to 60%.

.5. The process of claim 1 further characterized-in that theconcentration of polymer in the body of latex is above 55%.

' ;6. In the process for the preparation of shaped articles fromsynthetic latex, the steps which comprise dipping a smooth-surfaced forminto a body of an alkaline synthetic latex, the dispersed phase of whichlatex comprises 57 to 60% by weight of substantiallycompletelypolymerized chloro-2-butadiene-L3 polymer, said latex alsocomprising 1% by weight, based on the polymer, ofphenyl-p-naphthylamine, then. withdrawing the form slowly and at an evenspeed from the body of the latex, thereby retaining a coating of latexon the form, dipping the form in.a co,- agulating bath composed oisubstantially 1 volume of concentratedghydrochloric acid and 4 volumesof ethyl alcohol, then washing oil. the coagulant with water,repeating-the dipping, coagulation and washing steps until a coating ofthe desired thickness is obtained, drying the coating and thereafterremoving it from the form. "l. The process of claim 1 furthercharacterized in that. the synthetic latex contains about 1% by weight,based on the polymer, of phemrlfl-naphthylamineand a subsantial amountof zinc oxide.

8. The process of claim 2 iurther characten' ized in that the syntheticlatex contains about 1% by weight, based on thepolymer, of phenyl--.p-naphthyiamine and a substantial amount of zinc oxide. s

9.The process of claim 2 further characterized in that the colloid iscasein.

Patent No. 2,076,949. a April 1a, 1937.

] may conform to the record of the case in the Patent Office.

CERTIFICATE OF CORRECTION.

JAMES \KIRBY.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,second column, line 48, for "ordinarly read ordinary; and page 4, secondcolumn; line" 28, claim 5, for thenumeral 4*"1" read 2; and that thesaid Letters Patent should be read with these corrections therein thatthe same Signed and sealed this 29th day of June, A. D. 1957.

h Henry Van Arsdale (Seal) r r Acting Commissioner of Patents.

